1. Field of the Invention
The present invention relates to a control device and a data storage device, for details, a control device configured to control data transfer between a host device, a first storage configured as a nonvolatile storage for storing data, and a second storage configured as a nonvolatile random access memory having faster write speed than the first storage, and a data storage having such a control device.
2. Description of the Prior Art
One proposed structure of a control device controls a FeRAM (Ferroelectric Random Access Memory) as a cache memory or HDD to store data from a PC system (see, for example, Non-Patent Document 1). In the structure, the FeRAM is configured as a nonvolatile random access memory maintaining data stored therein when a power supply is stopped. In this device, data in the FeRAM is not regularly needed to be evacuated to HDD in preparation to an unexpected stop power supply. This arrangement enables to increase amount of data stored to FeRAM, and to increase cash hit ratio.    Non-patent document 1: Daisaburo Takahashi et al. “A 128 Mb ChainFeRAM™ and System Designs for HDD Application and Enhanced HDD Performance”, IEEE Asian Solid-State Circuits Conference, Nov. 16-18, 2009, Taipei, Taiwan.
In the device described above, data is input from PC system relatively fast, and a write speed in writing the input data to the HDD is relatively low. When data is input from the PC system, acceptance of input of data from PC system is stopped at once. After the input data is written to the HDD, the acceptance of input of next data is restarted. In this case, a write speed in writing the input data from the PC system to the HDD is limited by a writing speed of the HDD. So it is desirable to have a large increase in data write speed.